Hillary Clinton has earned enough delegates to clinch the Democratic nomination for U.S. president, according to an Associated Press tally.
She achieved 2,383 delegates — the number needed to make her the nominee — thanks to her win in Puerto Rico and last-minute support from superdelegates, the AP reported Monday night.
It means Clinton is the first ever female nominee for a major U.S. political party.
But her rival Bernie Sanders swiftly questioned the tally, saying that the result relied upon superdelegates — party officials free to support whichever candidate they want — who are unable to vote until the party convention in July.
"There is nothing to concede," Sanders told KTVU Monday.
Sanders spokesman Michael Briggs said that the votes of superdelegates should not be counted before they actually vote.
"Our job from now until the convention is to convince those superdelegates that Bernie is by far the strongest candidate against Donald Trump," Briggs said.
The AP's announcement came ahead of Democratic primaries in Montana, New Mexico, California, North Dakota, South Dakota and New Jersey on Tuesday.
"This is an important milestone," Clinton campaign manager Robby Mook said in a statement Monday. "But there are six states that are voting Tuesday, with millions of people heading to the polls, and Hillary Clinton is working to earn every vote. We look forward to Tuesday night, when Hillary Clinton will clinch not only a win in the popular vote, but also the majority of pledged delegates."
Clinton added on Twitter on Monday night: "We’re flattered, @AP, but we've got primaries to win. CA, MT, NM, ND, NJ, SD, vote tomorrow!"
Last month, the AP also announced that Trump has reached the number of delegates necessary to take the GOP nomination.